Author Topic: Choosing my gears wisely  (Read 12157 times)

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Offline panic

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Re: Choosing my gears wisely
« Reply #15 on: November 08, 2007, 10:59:59 AM »
Doh!! Memory failure - thanks.
Yes, the external Laycock de Normanville OD can be used in intermediate gears, there is a chance that 3rd + OD is mid-way (or at least useful) between 3rd and 4th to reduce your 3-4 shift RPM drop (4th to OD will slow the engine down too much). If it's less than the 26% loss you have now it will help, but not much, the most common is .80, so you'd only get another 400 RPM. It may also help between 2nd & 3rd.
It's an ambitious project in itself, since it involves shortening the driveshaft, re-angling the pinion stub and/or engine height, new brackets to support the OD box?, floor mods. however: it will make a taller (4.22:1) gear streetable again.

An Eaton of the correct size can be had and installed for less than $500...
Rough sizing: Eaton turns about 2 × engine speed for best efficiency, so Eaton nominal size can be as small as 50% of engine size: a 1500cc engine can use an M45 (= 45", 737cc) at 2 × speed to get roughly 1 bar.

Offline Stan Back

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Re: Choosing my gears wisely
« Reply #16 on: November 08, 2007, 03:35:07 PM »
" . . . but I like the discipline that the rules bring to the effort . . ."

Boy -- we don't hear that very often here.

Stan
Past (Only) Member of the San Berdoo Roadsters -- "California's Most-Exclusive Roadster Club" -- 19 Years of Bonneville and/or El Mirage Street Roadster Records

Offline Milwaukee Midget

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Re: Choosing my gears wisely
« Reply #17 on: November 08, 2007, 09:33:18 PM »
True, but now we're talking different trannys altogether, with different ratios.  Yeah, the OD MGB tranny might be made to fit with a custom 948 bellhousing. There's probably somebody out there making 'em.

The OD is 0.82:1.

The MGB tranny has different ratios, so with the OD operating in each gear (bypassing the stock 1-2 electric lockout on the od), my ratios at the yoke effectively become:

1=   3.44:1
1od= 2.8208:1
2=   2.167:1
2od= 1.77694:1   
3=   1.382:1       
3od= 1.13324:1   
4=    1:1           
4od=  .82:1  (probably useless)

Compared to

1 = 3.200:1
2 = 1.916:1 
3 = 1.357:1 
4 = 1:1.

That's a bit more elegant - you don't fall off the table on the 3-4 shift, and if my math is close, I'd be looking at 5700 at the start of 3rd, 6200 at the start of 3rd OD, and 6100 going into 4th.       

Another advantage is that I've got that tranny out in the garage, which would let me do the Rivergate 5-speed swap into my MGB. 

I can hear her now - "Honey, why are both the MG's up on jackstands?"
"Problems are almost always a sign of progress."  Harold Bettes
Well, I guess we're making a LOT of progress . . .  :roll:

Offline Constant Kinetics

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Re: Choosing my gears wisely
« Reply #18 on: July 17, 2010, 11:26:23 PM »
Seems like a supercharger could add enough torque to the upper mid power band to build momentum right at the shift into overdrive. If you can find a cam with a peak torque curve about 5500RPM or so and a peak horsepower curve around 6800RPM (maybe a 292/312 split diff or so) the overdrive could probably give you an edge.
Wierd is good